The present invention relates to (a) methods for reducing water production from wellbores, (b) compositions used in such methods, and (c) enhanced recovery systems treated by such methods.
Permeable subterranean formations often contain water, in many instances in the form of aqueous brines. Because this water is capable of flowing through the formation under appropriate conditions, its presence sometimes interferes with the recovery of hydrocarbons, such as oil and gas, from the formation. For example, during the recovery of hydrocarbons through a wellbore drilled into the formation, water may flow from the formation into the wellbore, thereby reducing hydrocarbon production. Excessive water flow may render the production of hydrocarbons uneconomical or reduce reservoir pressure to such an extent that hydrocarbon recovery is impossible.
To counteract the presence of water in a subterranean formation, U.S. Pat. No. 4,572,295 (Walley) introduces a nonaqueous treatment agent into that portion of the subterranean formation in which water permeability is to be reduced. Walley's non-aqueous treatment agent comprises a hydrogel polymer or copolymer that is preferably suspended in a non-aqueous fluid carrier. The hydrogel polymer swells or absorbs water when contacted by the water present in the subterranean formation. The hydrogel polymers of Walley are preferably lightly crosslinked.